This secretive Silicon Valley firm is valued at more than $15 billion, but most folks have no idea what Palantir Technologies actually does. That might be because some of its biggest clients—the Federal Bureau of Investigation and the Central Intelligence Agency, among them—are not exactly looking for publicity.

The 11-year-old company, started by Stanford Law School graduate Alexander Karp in 2004, sells software to the U.S. government and Wall Street firms to mine massive data sets for intelligence and law-enforcement applications. This software can take wildly disparate mounds of data and transform it into maps, charts and other forms of intelligence. Palantir's engineers can then go through a client's data and spell out for them potential trouble, whether that means terrorism, financial fraud or human trafficking.

Though the private company doesn't release financials, 2014 revenues are estimated to be north of $450 million. Palantir has been able to raise so much venture capital money—more than $1 billion to date—that there's wonder whether it will need to go public. Backers include the government intelligence agency In-Q-Tel, Tiger Global and Founders Fund. PayPal co-founder Peter Thiel is Palantir's chairman and a partner at Founders Fund.

"We only do it because the mission is really cool. ... It's basically very simple. ... We tell people you can help save the world."-Alexander Karp, co-founder and CEO, Palantir Technologies